This invention relates to valve actuators and more particularly to fail safe vane type actuators utilizing a spring return mechanism to assure complete valve closure.
Valve actuators are used in all segments of industry to open and close valves. Vane type valve actuators provide efficient remote control for any type of rotary operation of ball, plug and butterfly valves, or other mechanisms such as dampers, switches or safety and flow control devices. Valve actuators may be electronic or pneumatic providing reliable remote operation of valves. Reliability is very important to an operator who utilizes valve actuators to cyclically open and close a plurality of valves. Therefore, there is an industry demand for actuators that are fail safe. By fail safe, it is meant that the actuator automatically closes the valve on electrical failure or loss of air. The prior art discloses fail safe pneumatic actuators. These prior art actuators utilize air accumulators or spring return mechanisms to assure valve closure. A disadvantage associated with the prior art actuators utilizing a spring return mechanism is that the total force imparted by the compressed air is not directed to opening the valve. In these prior art actuators, compressed air is employed to open the valve and to cock or compress the spring return mechanism. Generally, the compressed air enters the vane housing and simultaneously exerts a force against the vane and the spring return mechanism. Before the valve can be opened, the compressed air must exert a force exceeding the threshold force required to compress the spring return mechanism. In addition, the prior art actuators are generally complex and bulky structures utilizing multiport valves to direct the air flow. The present invention solves the disadvantages associated with these prior art actuators.